Carbonaceous material for hydrogen storage, and method for preparation thereof, carbonaceous material having hydrogen absorbed therein and method for preparation thereof, cell and fuel cell using carbonaceous material having hydrogen absorbed therein

ABSTRACT

The present invention provides a hydrogen-stored carbonaceous material obtained by storing hydrogen in a carbonaceous material heated at more than 230° C. under a pressure reducing atmosphere, a battery and a fuel cell using this hydrogen-stored carbonaceous material. The carbonaceous material is heated at more than 230° C. under the pressure reducing atmosphere so that its surface can be efficiently cleaned and an area where the surface of the carbonaceous material comes into contact with hydrogen atoms or hydrogen molecules is increased.

TECHNICAL FIELD

[0001] The present invention relates to a hydrogen-storing carbonaceousmaterial and a method for producing it, a hydrogen-stored carbonaceousmaterial and a method for producing it and a battery and a fuel cellusing a hydrogen-stored carbonaceous material, and more particularly toa hydrogen-storing carbonaceous material and a method for producing it,a hydrogen-stored carbonaceous material and a method for producing itand a battery using the carbonaceous-stored carbonaceous material and afuel cell using the hydrogen-stored carbonaceous material which arelight, can be repeatedly used, be safe and may not possibly causeproblems in view of resources and an environment.

BACKGROUND ART

[0002] There has been hitherto widely employed fossil fuel such asgasoline, light oil, etc. as the energy source for producing an electricpower as well as the energy source of motor vehicles or the like. Thefossil fuel not only may possibly degrade a global environment, but alsois exhaustible and dubious whether or not the fossil fuel can be stablysupplied.

[0003] Hydrogen has been paid attention to in place of the fossil fuelhaving the above described possibilities. The hydrogen is contained inwater, inexhaustibly exists on the earth and includes a large quantityof chemical energy per amount of material. Further, the hydrogen hasadvantages as a clean and inexhaustible energy source by which thefossil fuel is replaced, because the hydrogen does not discharge harmfulsubstances or global greenhouse gas or the like when it is used as theenergy source.

[0004] Especially recently, the fuel cell that an electric energy can betaken out from the hydrogen energy has been eagerly studied anddeveloped and it has been expected that the fuel cell is applied to alarge-scale power generation, an onsite private power generation, andfurther, to a power supply for a motor vehicle.

[0005] On the other hand, since the hydrogen is gaseous under ambienttemperature and ambient pressure, it is treated with more difficultythan liquid or solid. Since the density of the gas is extremely small ascompared with that of liquid or solid, the chemical energy of the gas issmall per volume. Further, it is inconveniently difficult to store ortransport the gas. Still further, since the hydrogen is gas, it isliable to leak. When the hydrogen leaks, the danger of explosion isundesirably generated, which results in a great trouble in utilizationof the hydrogen energy.

[0006] Thus, in order to put an energy system using the hydrogen energyto practical use, the development of a technique that the gaseoushydrogen is efficiently and safely stored in a small volume has beenpromoted. There have been proposed a method for hydrogen storage as highpressure gas, a method for hydrogen storage as liquefied hydrogen and amethod for using a hydrogen-storing material, or the like.

[0007] In the method for hydrogen storage as the high pressure gas,since a very strong metallic pressure proof vessel such as a cylinderneeds to be used as a storage vessel, the vessel itself becomesextremely heavy and the density of the high pressure gas is ordinarilyabout 12 mg/cc. Accordingly, not only the storage density of thehydrogen is disadvantageously terribly small and a storage efficiency islow, but also there has a problem in view of safety because of highpressure.

[0008] On the contrary, in the method for hydrogen storage as theliquefied hydrogen, the storage density is ordinarily about 70 mg/cc.Although the storage density is considerably high, it is necessary tocool hydrogen down to lower than −250° C. in order to liquefy, so thatan additional device such as a cooling device is required. Therefore,not only a system has been undesirably complicated, but also energy forcooling has been needed.

[0009] Further, hydrogen-stored alloys are most effective materialsamong the hydrogen-stored materials. For instance, there have been knownlanthanum-nickel, vanadium, and magnesium hydrogen-stored alloys. Thepractical hydrogen storage density of these hydrogen-stored alloys isgenerally 100 mg/cc. Although the hydrogen is stored in thesehydrogen-stored alloys, the hydrogen storage density of these alloys isnot lower than that of liquefied hydrogen. Therefore, the use of thehydrogen-storing materials is the most efficient among conventionalhydrogen storage methods. Further, when the hydrogen-storing alloy isused, the hydrogen can be stored in the hydrogen-storing alloy and thehydrogen can be discharged from the hydrogen-storing alloy at aroundroom temperature. Further, since the hydrogen storage condition iscontrolled under the balance of the partial pressure of hydrogen, thehydrogen-storing alloy is advantageously treated more easily than thehigh pressure gas or the liquefied hydrogen.

[0010] However, since the hydrogen-stored alloys consist of metallicalloys, the are heavy and the amount of stored hydrogen is limited toapproximately 20 mg/g per unit weight, which may not be said to besufficient. Further, since the structure of the hydrogen-storing alloyis gradually destroyed in accordance with the repeated the cycle ofstoring and discharging of hydrogen gas, a performance is undesirablydeteriorated. Still further, there may be possibly generated fears ofthe problems of resources and an environment depending on thecomposition of the alloy.

[0011] Thus, for overcoming the above described issues of theconventional methods for hydrogen storage, a carbon material is paidattention to as the hydrogen-storing material.

[0012] For example, Japanese Patent Application Laid-Open No. hei.5-270801 proposes a method that the addition reaction of hydrogen isapplied to fullerene to store hydrogen. In this method, since a chemicalbond such as a covalent bond is formed between a carbon atom and ahydrogen atom, this method is to be called an addition of hydrogenrather than a hydrogen storage. Since the upper limit of the amount ofhydrogen which can be added by the chemical bonds is essentiallyrestricted to the number of unsaturated bonds of carbon atoms, theamount of stored hydrogen is limited.

[0013] Further, Japanese Patent Application Laid-Open No. hei. 10-72291proposes a technique that fullerene is used as the hydrogen-storingmaterial and the surface of the fullerene is covered with catalyticmetal such as platinum deposited by a vacuum method or a sputteringmethod to store hydrogen. In order to employ platinum as the catalyticmetal and cover the surface of fullerene with it, much platinum needs tobe used so that not only a cost is increased, but also a problem isgenerated in view of resources.

[0014] The method for hydrogen storage known heretofore is difficult tosay as a practical one when hydrogen energy is utilized. Especially,when the hydrogen energy is employed as an energy source for motorvehicles, marine vessels, general domestic power supplies, various kindsof small electric devices, etc. or when a large amount of hydrogen needsto be conveyed, the conventional methods for hydrogen storage is notpractical.

DISCLOSURE OF THE INVENTION

[0015] It is an object of the present invention to provide ahydrogen-storing carbonaceous material and a method for producing it, ahydrogen-stored carbonaceous material and a method for producing it anda battery and a fuel cell using a hydrogen-stored carbonaceous materialwhich are light, can be repeatedly used, are safe and may not possiblygenerate problems in view of resources and an environment.

[0016] The inventors of the present invention eagerly studied and foundthat the above described object of the present invention was achieved bya hydrogen-storing carbonaceous material obtained by heating thecarbonaceous material at more than 230° C. in a pressure reducingatmosphere.

[0017] In order to store a large amount of hydrogen in the carbonaceousmaterial, it is an important factor to increase an area where thesurface of the carbonaceous material comes into contact with hydrogenatoms or hydrogen molecules when a storing is carried out in the form ofa chemisorption or when the storing is carried out in the form of aproton storage. Therefore, it is important to clean the surface of thecarbonaceous material and efficiently remove impurities on the surface.It is known a report that the carbonaceous material is subjected to aheating process at 150° C. or 220° C. under a vacuum for the purpose ofremoving water content existing on the surface of a sample (forinstance, Appl. Phys. Let., by Y. Ye. et. al., Vol. 74, No. 16, (1999)2307-2309). In order to more improve a hydrogen storage capacity, it isnecessary to remove not only the water content, but also functionalgroups or metallic oxides or the like and increase an area where thesurface of the material comes into contact with hydrogen. According tothe study of the inventors of the invention from this point of view, itwas found that the carbonaceous material was heated at 230° C. or higherin the pressure reducing atmosphere so that the surface of thecarbonaceous material was efficiently cleaned and the area where thesurface of the carbonaceous material came into contact with the hydrogenatoms or the hydrogen molecules could be greatly increased. The presentinvention was invented on the basis of the above described knowledge.

[0018] The present has, as an object, the provision of ahydrogen-storing carbonaceous material by heating the carbonaceousmaterial at more than 230° C. under a pressure reducing atmosphere.

[0019] Further, the present invention provides a hydrogen-storedcarbonaceous material obtained by storing hydrogen in the carbonaceousmaterial heated at more than 230° C. under the pressure reducingatmosphere.

[0020] The hydrogen-stored carbonaceous material according to thepresent invention is obtained by heating the carbonaceous material atmore than 230° C. in the pressure reducing atmosphere to store hydrogen.

[0021] Further, the present invention concerns a battery having ananode, a cathode, an electrolyte interposed therebetween, and the anodeand/or the cathode includes a hydrogen-stored carbonaceous materialobtained by storing hydrogen in the carbonaceous material heated at morethan 230° C. under the pressure reducing atmosphere.

[0022] When a battery of the present invention is applied to an alkalinestorage battery in which aqueous alkaline solution such as potassiumhydroxide solution is employed for the electrolyte, a proton moves tothe anode from the cathode through the aqueous alkaline solution tostore the proton in the anode during a charging process. The proton canbe moved to the cathode side from the anode side through the aqueousalkaline solution during a discharging process. Further, when thepresent invention is applied to a hydrogen-air fuel cell in whichperfluorosulfonic acid polymer electrolyte film or the like is used forthe electrolyte, a proton previously stored in a hydrogen electrode by acharging or storing process is supplied to an air electrode through thepolymer electrolyte film during the discharging process. Accordingly, inthe hydrogen-air fuel cell, an electric power can be stably taken out.

[0023] Further, the present invention concerns a fuel cell comprising alaminated structure having an anode, a proton conductor and a cathode,and a hydrogen storage part including a hydrogen-stored carbonaceousmaterial obtained by heating the carbonaceous material at more than 230°C. under the pressure reducing atmosphere to store hydrogen, dischargingthe hydrogen and supplying it to the anode.

[0024] Since the fuel cell according to the present invention has thelaminated structure of the anode, the proton conductor and the cathode,and the hydrogen storage part including the hydrogen-stored carbonaceousmaterial obtained by heating the carbonaceous material under theatmosphere of gas including hydrogen gas and substantially including noreactive gas as impurity gas to store hydrogen, discharging hydrogen andsupplying it to the anode, the hydrogen discharged from the hydrogenstorage part produces a proton in accordance with a catalytic action inthe anode. The produced proton moves to the cathode together with aproton produced by the proton conductor so that the protons combine withoxygen to produce water and generate an electromotive force. Thus,according to the present invention, there can be provided the fuel cellin which the hydrogen can be more efficiently supplied than a case inwhich the hydrogen storage part is not provided and the conductivity ofthe protons is improved.

[0025] In the present invention, the hydrogen used and stored in thecarbonaceous material includes not only hydrogen molecules and hydrogenatoms, but also a proton as the atomic nucleus of hydrogen.

[0026] The pressure reducing atmosphere in the present inventiondesignates an atmosphere of 1.01×10⁴ Pascal, preferably 1.01×10² Pascal,and more preferably 1.01×10 Pascal.

[0027] The carbonaceous material employed in the present invention ispreferably heated at lower than 1500° C. Further preferably, thecarbonaceous material is heated at from 400° C. to 800° C.

[0028] As the carbonaceous material employed for the present invention,a carbonaceous material having a large surface and a structuralcurvature is selected. According to the study of the inventors of thepresent invention, since the carbonaceous material belongs to a σ-πnon-orthogonal electron system, it is found that HOMO and LUMO are lowerthan those of a σ-π orthogonal electron system. Therefore, thecarbonaceous material with the curvature can become a strong electronacceptor and separate the hydrogen into an electron and a proton (atomicnucleus of hydrogen) to store the hydrogen with high density in the formof the proton having no volume.

[0029] Further, the carbonaceous material in the present invention ispreferably composed of a carbonaceous material selected from a groupincluding fullerene, carbon nanofiber, carbon nanotube, carbon soot,nanocapsule, bucky onion and carbon fiber. As the fullerene, anyspheroidal carbon molecules may be used and all spheroidal carbonmolecules having the number of carbons such as 36, 60, 70, 72, 74, 76,78, 80, 82, 84, etc. can be utilized.

[0030] Still further, the carbonaceous material used in the presentinvention includes on its surface fine particles made of metal or ametallic alloy having a function for separating hydrogen atoms fromhydrogen molecules, or further, separating protons and electrons fromthe hydrogen atoms. The average size of the fine particles made of themetal or the alloy is desirably 1 micron or smaller. As the metal, thereis preferably employed metal or an alloy selected from a group includingiron, rare earth elements, nickel, cobalt, palladium, rhodium, platinumor alloys composed of one or two or more of these metals.

[0031] When the carbonaceous material having the curvature of fullerene,carbon nanofiber, carbon nanotube, carbon soot, nanocapsule, bucky onionand carbon fiber or the like is produced by an arc discharge method, themetal or the alloy thereof is preferably mixed into a graphite rodbefore the arc discharge. At the time of the arc discharge, the abovedescribed metals or the alloys thereof are allowed to exist, the yieldof the carbonaceous material can be enhanced and the hydrogen-storingcarbonaceous material with the curvature can be urged to be produced inaccordance with the catalytic action of these metals or the alloythereof. It has been known that these metals or the alloys thereofperform a catalytic action when the carbonaceous material such asfullerene, carbon nanofiber, carbon nanotube and carbon fiber or thelike is produced by a laser ablation method. The carbonaceous materialsuch as fullerene, carbon nanofiber, carbon nanotube and carbon fiber orthe like may be collected, added to and mixed with the hydrogen-storingcarbonaceous material so that the surface of the hydrogen-storingcarbonaceous material includes these metals or the alloys thereof.

[0032] In the present invention, the carbonaceous material includingthese metals or alloys thereof or the carbonaceous material including nometal or no alloy carries at least on its surface metallic fineparticles of 10 wt % or less which have a catalyzing function forseparating hydrogen atoms from hydrogen molecules, and further,separating protons and electrons from the hydrogen atoms. As apreferable metal having such a catalyzing function, there may beexemplified platinum or a platinum alloy, etc. In order to carry thesemetals on the surface of the carbonaceous material, a well-known methodsuch as a sputtering method, a vacuum deposition method, a chemicalmethod, a mixture or the like may be used.

[0033] Further, when platinum fine particles or platinum alloy fineparticles are carried on the carbonaceous material, a chemicallycarrying method using solution containing platinum complexes or an arcdischarge method using electrodes including platinum may be appliedthereto. In the chemically carrying method, for instance, chloroplatinicacid solution is treated with sodium hydrogen sulfite or hydrogenperoxide, then, the carbonaceous material is added to the resultantsolution and the solution is agitated so that the platinum fineparticles or the platinum alloy fine particles can be carried on thecarbonaceous materials. On the other hand, in the arc discharge method,the platinum or the platinum alloy is partly attached to the electrodepart of the arc discharge, and is subjected to the arc discharge to beevaporated so that the platinum or the platinum alloy can be adhered tothe carbonaceous material housed in a chamber.

[0034] The above described metals or the alloys thereof are carried onthe carbonaceous material, so that the hydrogen storage capacity can bemore improved than that when the metals or the alloys thereof are notcarried on the carbonaceous material. Further, it is found that anfluorine serving as an electron donor or an amine molecule such asammonia is mixed or combined with the carbonaceous material toefficiently generate a charge separation.

[0035] As described above, hydrogen composed of protons and electrons issupplied to the hydrogen-storing carbonaceous material as a strongelectron acceptor on which the above mentioned metals or the alloys aremounted, hence the hydrogen is stored in the form of protons. Therefore,its occupied volume is greatly reduced and a large amount of hydrogencan be stored in the hydrogen-storing carbonaceous material as comparedwith the storage by the conventional chemisorption of hydrogen atoms.That is, the hydrogen is separated into electrons and protons from thestate of atoms, and the electrons are efficiently stored in thehydrogen-storing carbonaceous material so that a large amount of highdensity hydrogen can be finally stored in the state of protons.Accordingly, when the above described metals or the alloys are carriedon the surface of the hydrogen-storing carbonaceous material, thehydrogen can be more efficiently stored and a larger amount of hydrogencan be stored. The above described hydrogen-storing carbonaceousmaterial is light, easily transported, can be repeatedly employed ataround room temperature without generating a structural destruction andcan be safely handled. Further, the amount of use of a metallic catalystsuch as platinum can be reduced. The carbonaceous material such asfullerene serving as a starting material can be also produced at a lowcost. Further, there can be realized an excellent practicability that aproblem is not found in view of the procurement of resources nor aproblem such as an environmental destruction is generated during a use.

[0036] Still further objects and specific advantages obtained by thepresent invention will become more apparent from the description ofembodiments or examples explained hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIG. 1 is a diagram showing a schematic structure of a fuel cellaccording to the present invention.

[0038]FIG. 2.is a diagram showing a schematic structure of an alkalinestorage battery (secondary battery) to which the present invention isapplied.

[0039]FIG. 3 is a graph showing the cyclic characteristics of thealkaline storage battery according to the present invention.

[0040]FIG. 4 is a diagram showing a schematic structure of ahydrogen-air fuel cell according to the present invention.

[0041]FIG. 5 is a graph showing the discharge characteristics of thehydrogen-air fuel cell according to the present invention.

[0042]FIG. 6 is a graph showing the discharge characteristics of ananother hydrogen-air fuel cell according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0043] Now, the specific configurations of a fuel cell and a secondarybattery using a carbonaceous material according to the present inventionwill be described by referring to the accompanying drawings.

[0044] The fuel cell according to the present invention is provided witha cathode 1 and an anode 2 arranged so as to be opposed to each other asshown in FIG. 1. Here, as the cathode 1, an oxygen electrode is used. Asthe anode 2, a fuel electrode or a hydrogen electrode is used. Thecathode 1 has a cathode lead 3 and a catalyst 5 is dispersed in thecathode or is adhered to the cathode. The anode 2 also has an anode lead6 and a catalyst 7 is dispersed in the anode or is adhered to the anode.A proton conductor 8 is sandwiched in between the cathode 1 and theanode 2. Hydrogen 12 as fuel is supplied to a passage 13 in the side ofthe anode 2 through an introducing port 11 from a hydrogen supply source10, and discharged from a discharge port 14. In the side of the cathode1, air 15 is supplied to a passage 17 from an introducing port 16 anddischarged from a discharge port 18.

[0045] While the hydrogen 12 serving as the fuel supplied to the passage13 from the introducing port 11 passes the passage 13, protons aregenerated and the generated protons move to the side of the cathode 1together with protons generated in the proton conductor 8. As a result,the protons react with oxygen in the air 15 supplied to the passage 17from the introducing port 16 and directed to the discharge port 18 sothat a desired electromotive force is taken out.

[0046] In the present invention, for the hydrogen supply source 10, isemployed a hydrogen-stored carbonaceous material obtained by heating acarbonaceous material such as fullerene, carbon nanofiber, carbonnanotube, carbon soot, nanocapsule, bucky onion and carbon fiber or thelike at more than 23° C. in the pressure reducing atmosphere and thenstoring hydrogen.

[0047] In the fuel cell according to the present invention, since, whilethe protons are dissociated, the protons supplied from the anode 2 sidemove to the cathode 1 side in the proton conductor 8, the conductivityof the protons is characteristically improved. Therefore, since ahumidifier which has been hitherto required for conducting protons isnot needed, a system can be simplified and lightened.

[0048] For more clearly describing the effects of the present invention,examples and comparative examples of the present invention will bementioned below.

EXAMPLE 1

[0049] A carbon nanofiber with one nanotube fiber whose diameter isabout 200 nm was manufactured by a CVD method and impurities such as acatalyst were completely removed until purity became 95% or higherbefore a thermobalance measurement was carried out. The carbon nanofiberof 15.4 mg thus obtained was accommodated in a sample cup in athermobalance, and then, while pressure was reduced by a rotary pump,the temperature of the carbon nanofiber was raised up to 230° C. at arate of 60° C. per minute and held at 230° C. for 4 hours to clean thecarbon nanofiber.

[0050] After the cleaning process was finished, the temperature waslowered to 20° C. After it was recognized that the temperature of thecarbon nanofiber reached 20° C., hydrogen gas was introduced to themeasurement vessel to measure the change of the mass of the carbonnanofiber. Thus, it was found that the hydrogen of 1.2 wt % was stored.

EXAMPLE 2

[0051] After a carbon nanofiber was cleaned in the absolutely samemanner as that of the Example 1 except that the carbon nanofiber washeated up to 400° C. and held at 400° C. for 3 hours to clean the carbonnanofiber under the pressure reducing atmosphere, the carbon nanofiberwas cooled to 20° C. After it was recognized that the temperature of thecarbon nanofiber reached 20° C., hydrogen gas was introduced to themeasurement vessel to measure the change of the mass of the carbonnanofiber.

[0052] In such a manner, when the amount of stored hydrogen in thecarbon nanofiber was obtained, it was found that hydrogen of 2.2 wt %was stored in the carbon nanofiber.

EXAMPLE 3

[0053] After a carbon nanofiber was cleaned in the absolutely samemanner as that of the Example 1 except that the carbon nanofiber washeated up to 800° C. and held at 800° C. for 3 hours to clean the carbonnanofiber under the pressure reducing atmosphere, the carbon nanofiberwas cooled to 20° C. After it was recognized that the temperature of thecarbon nanofiber reached 20° C., hydrogen gas was introduced to themeasurement vessel to measure the change of the mass of the carbonnanofiber.

[0054] In such a manner, when the amount of stored hydrogen in thecarbon nanofiber was obtained, it was found that hydrogen of 2.1 wt %was stored in the carbon nanofiber.

EXAMPLE 4

[0055] After a carbon nanofiber was cleaned in the absolutely samemanner as that of the Example 1 except that the carbon nanofiber washeated up to 1400° C. and held at 1400° C. for 3 hours to clean thecarbon nanofiber under the pressure reducing atmosphere, the carbonnanofiber was cooled to 20° C. After it was recognized that thetemperature of the carbon nanofiber reached 20° C., hydrogen gas wasintroduced to the measurement vessel to measure the change of the massof the carbon nanofiber.

[0056] In such a manner, when the amount of stored hydrogen in thecarbon nanofiber was obtained, it was found that hydrogen of 0.4 wt %was stored in the carbon nanofiber.

COMPARATIVE EXAMPLE 1

[0057] A carbon nanofiber was manufactured in the same manner as that ofthe Example 1 and impurities such as a catalyst were completely removeduntil purity became 95% or higher before a thermobalance measurement wascarried out.

[0058] The carbon nanofiber of 15.4 mg thus obtained was accommodated ina sample cup in a thermobalance, and then, initially, the contents in ameasurement vessel were completely replaced by using nitrogen gas.

[0059] Then, hydrogen gas of 1 atmospheric pressure was introduced intothe measurement vessel at a flow velocity of 100 cc per minute and heldfor 3 hours.

[0060] Subsequently, nitrogen gas was introduced again into themeasurement vessel to measure the change of the mass of the carbonnanofiber.

[0061] As a result, the change of the mass was not recognized. Thus, itwas found that hydrogen was not stored.

COMPARATIVE EXAMPLE 2

[0062] After a carbon nanofiber was manufactured in the absolutely samemanner as that of the Example 1 and impurities such as a catalyst werecompletely removed until purity became 95% or higher before athermobalance measurement was carried out.

[0063] The carbon nanofiber of 15.4 mg thus obtained was accommodated ina sample cup in a thermobalance, then, while the pressure was reduced bya rotary pump, the carbon nanofiber was heated up to 200° C. at a rateof 60° C. per minute and held at 200° C. for 4 hours to clean the carbonnanofiber.

[0064] After the cleaning operation, the carbon nanofiber was cooled to20° C. After it was recognized that the temperature of the carbonnanofiber reached 20° C., hydrogen gas was introduced to the measurementvessel to measure the change of the mass of the carbon nanofiber. Thus,it was recognized that the hydrogen of 0.2 wt % was stored in the carbonnanofiber.

[0065] It was understood from the Examples 1 to 4 and the ComparativeExamples 1 and 2 that while the carbon nanofiber subjected to noprocessing had no hydrogen storage capacity and the carbon nanofibercleaned at the temperature of 200° C. in the pressure reducingatmosphere had only a hydrogen storage capacity of 0.2 wt %, thehydrogen storage capacity of the carbon nanofiber cleaned by the carbonmonoxide gas of 1 atmospheric pressure under from 230° C. to 1400° C.was improved, and the above described effect was obviously improvedespecially at from 400° C. to 800° C.

EXAMPLE 5

[0066] An alkaline storage battery was manufactured in the followingmanner.

[0067] <Manufacture of Cathode>

[0068] Carboxymethyl cellulose of 3 wt % was added to spherical nickelhydroxide of 10 g with the average particle size of 30 μm and cobalthydroxide of 1 g and the mixture was kneaded with water to preparepaste. A porous nickel foam with the porosity of 95% was filled with thepaste, and the porous nickel foam filled with the paste was dried andpressed, and then punched to manufacture a cathode having the diameterof 20 mm and the thickness of 0.7 mm.

[0069] <Manufacture of Anode>

[0070] Carboxymethyl cellulose of 5% and water were added to thehydrogen-stored carbonaceous material which prepared in accordance withthe Example 2 to prepare kneaded paste. The porous nickel foam with theporosity of 95% was filled with the paste, the porous nickel foam filledwith the paste was dried and pressed, and then punched to manufacture ananode with the diameter of 20 mm and the thickness of 0.5 mm.

[0071] <Alkaline Storage Battery>

[0072] Then, an alkaline storage battery (secondary battery)schematically shown in FIG. 2 was manufactured by using the cathode andthe anode manufactured as described above and potassium hydroxidesolution of 7N as electrolyte solution.

[0073] The alkaline storage battery comprises a cathode 1, an anode 2and electrolyte solution 21 contained therebetween in a battery vessel20. A cathode lead 3 and an anode lead 6 are taken outside the batteryvessel 20 from the respective electrodes.

[0074] <Charge and Discharge Performance>

[0075] For the alkaline storage battery manufactured as described above,the charge and discharge test was carried out with 0.1C, the upper limitof 1.4V and the lower limit of 0.8 V. The cyclic characteristics at thattime are shown in FIG. 3.

[0076] As apparent from FIG. 3, although it could not be said that acycle life was not sufficient from the viewpoint of structure of thebattery, a basic charge and discharge performance could be recognized.

EXAMPLE 6

[0077] A hydrogen-air fuel cell was manufactured in the followingmanner.

[0078] <Manufacture of Air Electrode>

[0079] The hydrogen-stored carbonaceous material was prepared inaccordance with the Example 2. The hydrogen-stored carbonaceous materialand polymer electrolyte alcoholic solution composed of perfluorosulfonicacid were dispersed in n-butyl acetate to prepare catalyst layer slurry.

[0080] On the other hand, a carbon nonwoven fabric with the thickness of250 μm was immersed in the emulsion of fluorine water repellent, driedand then heated at 400° C., so that the carbon nonwoven fabric wassubjected to a water repellent process. Subsequently, the carbonnonwoven fabric was cut to the size of 4 cm×4 cm and the catalyst layerslurry prepared as described above was applied to one surface thereof.

[0081] <Adhesion of Air Electrode to Polymer Electrolyte Film>

[0082] A polymer electrolyte film composed of perfluorosulfonic acidwith the thickness of 50 μm was adhered to the surface of the carbonnonwoven fabric to which the catalyst layer was applied, and then, thefilm adhered to the nonwoven fabric was dried.

[0083] <Manufacture of Hydrogen Electrode>

[0084] Carboxymethyl cellulose of 5% and water were added to the samehydrogen-stored carbonaceous material as that used for manufacturing theair electrode to prepare paste. A porous nickel foam with the porosityof 95% was filled with the paste, dried and pressed and the dried andpressed porous nickel foam was cut to the size of 4 cm×4 cm tomanufacture a hydrogen electrode with the thickness of 0.5 mm.

[0085] <Manufacture of Hydrogen-Air Fuel Cell>

[0086] The hydrogen electrode was superposed on the adhered body of theair electrode and the perfluorosulfonic acid polymer electrolyte filmobtained as described above by holding the polymer electrolyte filmtherebetween. Both the surfaces thereof were firmly held by Teflonplates with the thickness of 3 mm and fixed by bolts. Many holes withdiameter of 1.5 mm are previously opened on the Teflon plate arranged inthe air electrode side so that air can be smoothly supplied to anelectrode.

[0087] The schematic structure of the hydrogen-air fuel cell thusassembled is shown in FIG. 4.

[0088] As shown in FIG. 4, in the hydrogen-air fuel cell thusmanufactured, a hydrogen electrode 31 and an air electrode 32 arearranged so as to be opposed to each other by locating a polymerelectrolyte film 30 between the hydrogen electrode and the airelectrode. The outer side of these members is held by a Teflon plate 33and a Teflon plate 35 provided with many air holes 34 and all the bodyis fixed by means of bolts 36 and 36. A hydrogen electrode lead 37 andan air electrode lead 38 are respectively taken out from the respectiveelectrodes.

[0089] <Discharge Characteristics of Hydrogen-Air Fuel Cell>

[0090] Then, the discharge characteristics of the hydrogen-air fuel cellwas examined.

[0091] Initially, electric current was supplied in a charging directionwith the current density of 1 mA/cm² to store hydrogen in the hydrogenelectrode. Then, a discharging operation was carried out with thecurrent density of 1 mA/cm². As a result, the discharge characteristicsas shown in FIG. 5 could be obtained and a function as the hydrogen-airfuel cell was recognized.

[0092] Further, before the fuel cell was assembled, hydrogen waspreviously stored in the hydrogen electrode under the pressure of 100kg/cm². The hydrogen electrode thus hydrogen storage was superposed onthe adhered body of the air electrode and the perfluorosulfonic acidpolymer electrolyte film obtained as described above to assemble thehydrogen-air fuel cell. When the discharge characteristic of theobtained fuel cell was measured with the current density of 1 mA/cm²,the discharge characteristic as shown in FIG. 6 was obtained and afunction as the hydrogen-air fuel cell could be also recognized in thiscase.

[0093] It is to be understood that the present invention is not limitedto the above described embodiments and Examples and various kinds ofchanges may be performed within the scope of the present inventiondefined in claims and they may be also involved in the scope of theinvention.

[0094] For example, in the above described embodiments, although thefuel cell using the hydrogen-storing carbonaceous material and thehydrogen-stored carbonaceous material was described, thehydrogen-storing carbonaceous material and the hydrogen-storedcarbonaceous material according to the present invention are not limitedto the fuel cell but also may be widely applied to uses for hydrogenstorage as well as other batteries such as an alkaline storage battery,a hydrogen-air fuel cell, etc.

[0095] Industrial Applicability

[0096] According to the present invention, there can be provided ahydrogen-storing carbonaceous material which can efficiently store alarge amount of hydrogen, is light and safe, can be repeatedly used andmay not possibly generate problems in view of resources and anenvironment and a method for producing it, a hydrogen-storedcarbonaceous material and a method for producing it, a battery using ahydrogen-stored carbonaceous material and a fuel cell using ahydrogen-stored carbonaceous material.

1. A hydrogen-storing carbonaceous material obtainable by heating acarbonaceous material at more than 230° C. under the pressure reducingatmosphere.
 2. The hydrogen-storing carbonaceous material according toclaim 1, obtainable by heating the carbonaceous material at from 400° C.to 800° C.
 3. The hydrogen-storing carbonaceous material according toclaim 1, wherein the carbonaceous material has a large surface and astructural curvature.
 4. The hydrogen-storing carbonaceous materialaccording to claim 3, wherein the carbonaceous material is selected froma group consisting of fullerene, carbon nanofiber, carbon nanotube,carbon soot, nanocapsule, bucky onion and carbon fiber.
 5. A producingmethod of a hydrogen-storing carbonaceous material comprising a step ofheating a carbonaceous material at more than 230° C. under the pressurereducing atmosphere.
 6. The producing method of a hydrogen-storingcarbonaceous material according to claim 5, obtainable by heating thecarbonaceous material at from 400° C. to 800° C.
 7. The producing methodof a hydrogen-storing carbonaceous material according to claim 5,wherein the carbonaceous material has a large surface and a structuralcurvature.
 8. The producing method of a hydrogen-storing carbonaceousmaterial according to claim 7, wherein the carbonaceous material isselected from a group consisting of fullerene, carbon nanofiber, carbonnanotube, carbon soot, nanocapsule, bucky onion and carbon fiber.
 9. Ahydrogen-stored carbonaceous material obtainable by storing hydrogen ina carbonaceous material heated at more than 230° C. under the pressurereducing atmosphere.
 10. The hydrogen-stored carbonaceous materialaccording to claim 9, obtainable by heating the carbonaceous material atfrom 400° C. to 800° C.
 11. The hydrogen-stored carbonaceous materialaccording to claim 9, wherein the carbonaceous material has a largesurface and a structural curvature.
 12. The hydrogen-stored carbonaceousmaterial according to claim 11, wherein the carbonaceous material isselected from a group consisting of fullerene, carbon nanofiber, carbonnanotube, carbon soot, nanocapsule, bucky onion and carbon fiber.
 13. Aproducing method of a hydrogen-stored carbonaceous material comprising astep of storing hydrogen in a carbonaceous material heated at more than230° C. under the pressure reducing atmosphere.
 14. The producing methodof a hydrogen-stored carbonaceous material according to claim 13,obtainable by heating the carbonaceous material at from 400° C. to 800°C.
 15. The producing method of a hydrogen-stored carbonaceous materialaccording to claim 13, wherein the carbonaceous material has a largesurface and a structural curvature.
 16. The producing method of ahydrogen-stored carbonaceous material according to claim 15, wherein thecarbonaceous material is selected from a group consisting of fullerene,carbon nanofiber, carbon nanotube, carbon soot, nanocapsule, bucky onionand carbon fiber.
 17. A battery having an anode, a cathode and anelectrolyte provided therebetween, wherein the anode and/or the cathodeincludes a hydrogen-stored carbonaceous material obtainable by storinghydrogen in a carbonaceous material heated at more than 230° C. underthe pressure reducing atmosphere.
 18. The battery according to claim 17,obtainable by heating the carbonaceous material at from 400° C. to 800°C.
 19. The battery according to claim 17, wherein the carbonaceousmaterial has a large surface and a structural curvature.
 20. The batteryaccording to claim 19, wherein the carbonaceous material is selectedfrom a group consisting of fullerene, carbon nanofiber, carbon nanotube,carbon soot, nanocapsule, bucky onion and carbon fiber.
 21. A fuel cellhaving a laminated structure of an anode, a proton conductor and acathode, and a hydrogen storage part including a hydrogen-storedcarbonaceous material obtainable by storing hydrogen in a carbonaceousmaterial heated at more than 230° C. under the pressure reducingatmosphere, discharging hydrogen and supplying it to the anode.
 22. Thefuel cell according to claim 21, obtainable by heating the carbonaceousmaterial at from 400° C. to 800° C.
 23. The fuel cell according to claim21, wherein the carbonaceous material has a large surface and astructural curvature.
 24. The fuel cell according to claim 23, whereinthe carbonaceous material is selected from a group consisting offullerene, carbon nanofiber, carbon nanotube, carbon soot, nanocapsule,bucky onion and carbon fiber.